1. Field of the Invention
The invention relates to a process for obtaining traffic data in a compressed form, while largely retaining the reliability of the data. A speed profile is determined for and in a vehicle moving in traffic, which belongs to a sampling vehicle fleet, and the data are transmitted wirelessly to a traffic center from time to time.
2. Discussion of the Prior Art
Such sampling fleet vehicles that move in traffic as measurement probes are called "floating cars." Using many such "floating cars," it is possible in principle to operate a system for obtaining traffic data. An effort is thereby made to collect the traffic situation data as completely as possible, so that information derived from the obtained data will be reliable and informative. The object of the invention is to provide a data base for traffic information, on the basis of which drivers can plan their driving movements, with respect to time and place, in such a way that their routes can be travelled in the shortest possible time and without interference from traffic jams, for example. To this end, it is important that the drivers be informed accurately and in a timely manner about existing or developing traffic jams, for instance. This is a central task of telematic traffic services provided to drivers via wireless communications paths.
When traffic situation data are collected, it is essential that changes in the current traffic situation in the immediate vicinity of a "floating car" be recognized by the "floating car" and transmitted to the traffic center as quickly as possible, so that the overall traffic picture can be kept as up-to-date as possible. When attempts are made to keep the sensor system of a "floating car" simple (for example, by not installing cameras or distance detectors in the car), perhaps for reasons of cost alone, the traffic environment in which the "floating car" finds itself is not visible. However, the speed data of the vehicle are easily detectable in the vehicle, and highly useful and generally adequate information can be obtained by continuously observing changes in these speed data. Unfortunately, when such speed data are transmitted to a traffic center, usually via the data transmission paths of a mobile telephone network, the abundance of data, and thus the load placed on the transmission channels, can be extraordinarily high, given the large number of sampling vehicles needed. As a result, the costs of implementing a suitable process for obtaining traffic data can assume a magnitude that precludes practical applicability. A series of proposals have therefore already been made on how to limit data volume. These efforts often entail, however, a conflict of goals that has not been satisfactorily resolved by previous processes. Specifically, in addition to the criterion of data completeness, the criteria of data volume minimality and data up-to-dateness must be taken adequately into account.
If "floating cars" report to the traffic center only periodically, it is usually possible, given suitably short reporting intervals, to obtain both data completeness and data up-to-dateness. However, the scope of transmitted data will not be minimal. If transmission intervals are lengthened, up-to-dateness suffers, while minimality is not actually achieved, because data of limited informative value will still be transmitted. In processes based on the identification of important traffic events by "fuzzy logic," the completeness of data collection is not ensured, because this procedure, by its nature, prevents any reconstruction of how the fuzzy-logic level was arrived at. Finally, data collection followed by approximation and information-theory compression (i.e., data compression without information loss) does not, as a rule, adequately meet the up-to-dateness criterion, because only when a large quantity of data is available can approximation and compression be carried out efficiently.